What a dark card still tells you
The Index is hotbar slot 3. Each area has a page. An uncaught Scroom is a black silhouette labelled ???, and the card can still show rarity and a frequency range. An area tab that is itself ??? means you have not entered that region. Those are different problems.
A completion percent on a screenshot is that player's progress. The Grove page has 15 cards. Bluestone Caverns has 15 cards, of which 14 names were readable and one silhouette was still unnamed. Do not treat someone else's 93% as your own.
Rarity is a label
The ladder runs Common, Uncommon, Rare, Wondrous, Fabled, Eversung. Rare is one tier. Players also say "rare" for anything above Common. A Wondrous or Fabled card is not the Rare tier under another name.
Eversung is the top label, not a creature called Eversung. The two named entries are The Pale Vessel in Grave of the Gilded and The Violet Fool in Sanctum Magus.
Across the 55 Scrooms placed on those five pages, the counts are 15 Common, 13 Uncommon, 13 Rare, 7 Wondrous, 5 Fabled, and 2 Eversung. Six more names are not on those pages: Craglin, Elder Goldoak, Glimwick, Nightfang, Regalith, and Vex.
Prefixes are not new species
Melodic, Harmonic, Resonant, Mossy, Wooden, Metallic, Frozen, Blazing, Runic, Verdant, and Charged are versions of a base Scroom. A Blazing Trufflecrust still fills Trufflecrust. Iblis is the exception to treat carefully: his quest asks for the Runic prefix on Sigilith, Inkling, and Occulot. A plain copy does not satisfy that objective.
Use the range on the card
Frequency is per species, not per rarity. Redcap and Florabella can share 18.7–31.2 Hz while one is Common and the other is Wondrous. Koroom's Grove card is 71.2–118.7 Hz. One reported catch was 85.5 Hz, inside that range. Older clips that quoted Koroom near 77 Hz, Burlcap near 37.4 Hz, or Faebud near 41 Hz were single readings. Where they fall outside the Index range, use the card.
Funglebee is reported on the grass below Beekeeper Jones's hives during a Pale Moon.
Pick one missing card in an area you can enter. If its range sits above your Resonance, that is a gear problem. If you can tune it and then lose the bar, that is a control problem. The full roster is under Scrooms.